A method for time synchronization between transmission devices which transmit frames via a transmission network includes, for example, the precision time protocol (PTP) defined in the IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 1588. In the precision time protocol, a time synchronization frame called a PTP message is exchanged between a transmission device and a master clock, thereby correcting an error between a clock on the transmission device side and a clock of the master clock.
The related art is disclosed in Japanese Laid-open Patent Publication No. 2011-23788 or 10-336182.